Patent GB-905733-A (GB)
Title: Process for the manufacture of plastic film tube
IPC: B29C48/03
Filed: 1960-10-04
Abstract: In a method of making tubular film by extruding a thermoplastic resinous material through a tube die into a temperature regulating bath and maintaining a liquid column within the freshly extruded tube prior to flattening, a silicone fluid, liquid at the operating temperature, is used as the liquid column.  The liquid column may be held at an elevated temperature greater than that of the temperature regulating bath but not in excess of the extrusion temperature of the film.  Desirably the silicone fluid has a viscosity at 25 DEG C. between 5 and 100 centistokes, especially between 10 and 50 centistokes, and may be a polymer having repeating units of the general formula:-RnSiO 4-n/2 where R is a monovalent aromatic hydrocarbon radical or halogenated aromatic hydrocarbon radical with 6-10 carbon atoms, or a monovalent aliphatic hydrocarbon radical or halogenated aliphatic hydrocarbon radical with 1-8 carbon atoms, or a mixture thereof, and n lies between 1,95 and 2,2.  Specified silicone fluids are dimethyl siloxane polymers, diethyl siloxane polymers, and copolymers of phenylmethyl siloxane and dimethyl siloxane containing between 20 and 70 mole per cent of the former, and preferably containing equimolar proportions of the two constituents.  The film tube is preferably made of a normally crystalline vinylidene chloride polymer, or of a copolymer of at least 70% by weight vinylidene chloride with either vinyl chloride, or acrylonitrile.  Other specified polymers include polyvinyl chloride, vinyl chloride/vinyl acetate copolymers, chlorinated polyethylene, chlorinated polypropylene, chlorinated rubber, polystyrene, styrene/acrylonitrile copolymers, a -methyl styrene, ethyl acrylate, vinyl toluene and acrylonitrile polymers, cellulose acetate, cellulose acetate butyrate, polyethylene and polypropylene, polyamides and polyesters. The film may be subsequently oriented by inflation, slit and heat-shrunk in known manner.ALSO:A tubular film is made by extruding a thermoplastic resinous material through a tube die into a temperature regulating bath and maintaining a liquid column of a silicone fluid within the freshly extruded tube prior to flattening, and the tube is then oriented, slit, heat-shrunk and metallized with a layer of aluminium applied as a vapour under a vacuum of about 1 micron.  A perfectly smooth coating is thus obtained, without the need for washing after slitting and prior to heat-shrinkage, which arises when conventional mineral oils are used as the liquid column. Specified film materials include a normally crystalline vinylidene chloride polymer, or of a copolymer of at least 70% by weight vinylidene chloride with either vinyl chloride, or acrylonitrile. Other specified polymers include polyvinyl chloride, vinyl chloride/vinyl acetate copolymers, chlorinated polyethylene, chlorinated polypropylene, chlorinated rubber, polystyrene, styrene/acrylonitrile copolymers,  -methyl styrene, ethyl acrylate, vinyl toluene and acrylonitrile polymers, cellulose acetate, cellulose acetate butyrate, polyethylene and polypropylene, polyamides and polyesters.